RFR: JDK-8315458 Implement JEP 463: Implicitly Declared Classes and Instance Main Method (Second Preview) [v18]

[Jim Laskey]

> Address changes from JEP 445 to JEP 463.
> 
> - Move from a SYNTHETIC unnamed class to a MANDATED implicit class.
> 
> - Don't mark class on read.
> 
> - Remove reflection and annotation processing related to unnamed classes.
> 
> - Simplify main method search.

Jim Laskey has updated the pull request incrementally with one additional commit since the last revision:

  Reinstate test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16461/files
  - new: https://git.openjdk.org/jdk/pull/16461/files/abf48816..dd6703e7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16461&range=17
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16461&range=16-17

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16461.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16461/head:pull/16461

PR: https://git.openjdk.org/jdk/pull/16461